The present invention is directed to aircraft obstacle awareness systems, in general, and more particularly, to a distributed laser obstacle awareness system for use on an aircraft for the detection of ground and air based obstacles.
A common flight hazard of any aircraft operating near the Earth is the potential for collision with ground structures and obstacles. Helicopters, in particular, and now new classes of aircraft known as unmanned air vehicles (UAVs), often operate less than five hundred feet above ground level (AGL). In this environment, it is not uncommon for these aircraft to collide with electrical power lines, support wires for radio towers, or various structures and obstacles. These collisions typically result in loss of life, significant aircraft damage, damage to the structures or obstacles themselves, subsequent loss of power distribution on the electrical grid, and danger to persons and property on the ground. Aircraft, such as helicopters and UAVs, for example, typically operate in these low altitudes for take-off and landing, various low-level military maneuvers, and commercial applications, such as electrical utility inspection or emergency rescue missions.
Inspecting electrical power lines from an aircraft requires flying close to the Earth along high tension power lines and support structures looking for damaged equipment. Use of helicopters permit electric utility inspection crews to cover a large area of the power grids over a short period of time. Other helicopter applications which require low flying flight profiles include emergency and rescue missions, medical emergencies, border surveillance, and supply of floating oil platforms, for example. Likewise, UAV applications require autonomous control for surveillance, take-off, landing and delivery of munitions. In all of these applications, the flight crew and aircraft are at risk of colliding with obstacles like power lines, cables, towers, and other similar support structures. The risk becomes even greater with poor visibility and flights over unknown terrain. Depending on the type of aircraft canopy, the lighting, and the environmental conditions, many obstacles may become effectively invisible to the pilot and crew due to background clutter even under daylight conditions. Also, because of the narrow field of view offered the pilot by the aircraft, some obstacles may not be seen until it is too late for avoidance. Surprisingly, the highest accident rates are typically associated with clear conditions which indicates that during reduced states of pilot situational awareness, identification of hazardous ground obstacles may occur less regularly.
Some helicopters are equipped with structural wire strike protection kits which are fitted on the front end of the aircraft and intended to force a wire in the path of the aircraft to slide over the top or under the bottom of the aircraft. However, for this device to be effective, a contacted wire must slide across the canopy and into the wire cutters. When this occurs, the wire is likely to be severed by the wire cutter(provided it meets certain size and strength envelopes), freeing the aircraft from the hazards. It is not uncommon for electrical utility companies to identify cut wires but have no report of a wire strike accident. In some cases this indicates the flight crew did not know they hit a wire, much less cut it, or are reluctant to report the incident. However, if the wire does not slide across the canopy, and impacts other areas of the helicopter such as the rotors or landing skids, the wire cannot be severed by the wire strike protection system. As tension builds in the wire due to the forward motion, damage to the aircraft ensues with penetration into the canopy and flight crew, damage to the main rotor resulting in an imbalance, or loss of tail rotor control. In all these cases, the flight crew is in immediate life threatening danger. Depending upon the degree of interaction, fatalities can be attributed to the high-g accelerations of the rotor imbalance, blunt force trauma due to subsequent impact with the ground/aircraft, or harmful interactions with the wire resulting in significant lacerations or electrocution. Accordingly, due to the many low-level flying applications and the increasing risks posed thereby, obstacle avoidance warning systems for these aircraft have become of paramount importance for the safety of the pilot and crew of the aircraft. These devices are intended to warn the flight crew in advance of the collision with the obstacle, so that they(or an automated flight control system)can take evasive action prior to collision.
Thus, for manned aircraft, collisions with ground and air based obstacles result in numerous fatalities each year, while for UAVs, the aircraft can be lost, rendered uncontrollable, or unable to conduct the desired mission. Often UAV platforms are quite new with numerous sensors and signal intelligence suites. While mechanisms exist to render these devices useless to prevent a lost UAV from falling into enemy hands, lost UAVs can compromise mission capabilities and/or intent. Loss of mission control of a UAV or a precision guided munition (PGM) often results in the vehicle veering off course with unpredictable results, like hitting an unintended target, for example. Today, PGMs and UAVs are taking on a greater presence in military missions, often operating in densely packed urban environments and required to fly complex routes to avoid civilian causalities. In the future, there will be a greater reliance on PGMs and UAVs to successfully navigate a cluttered environment to find the target of interest without veering off course or colliding with unintended obstacles.
Amphitech International of Montreal, Canada, has developed a radar based obstacle awareness system named OASYS which was presented at the Quebec HeliExpo 2001. While it is proposed that OASYS can detect small obstacles, such as power lines, for example, up to two kilometers away even in adverse weather conditions, it is a rather heavy, bulky and costly unit, which may render it prohibitive for small aircraft usage.
Another obstacle awareness warning system is being developed by Dornier GmbH, in its Defense and Civil Systems Business Unit of Friedrichshafen, Germany under the tradename of HELLAS (Helicopter Laser Radar). In this unit, a laser beam is sequentially scanned through a line series of approximately one hundred optic fibers to create a raster line scan which is projected from the system. The line scan is steered vertically by a pivoted, oscillating mirror. The field-of-view is approximately plus and minus 32 degrees in azimuth and elevation with respect to a line of sight of the system. While Dornier promotes HELLAS as being an effective obstacle detection unit, it remains a relatively narrow field of view device that is rather complex and costly. In addition, the large number of optic fibers required for effective obstacle detection resolution, appears to render the device difficult to repeatedly align which may lead to manufacturing difficulties.
Another problem encountered in these low-level flight profile aircraft applications is the wind or air flow conditions surrounding the aircraft while it is carrying out its tasks. In some cases, an aircraft may encounter substantially different air-flow conditions from side to side. For example, when flying in a canyon, the aircraft may have a mountain wall on one side and open spaces on the other. Landing on the flight deck of an aircraft carrier poses similar risks. Such uneven air flow conditions may have an adverse affect on the responsiveness of the aircraft to the avoidance of detected obstacles.
Accordingly, it is desirable to have an obstacle awareness system that can be distributed through the aforementioned aircraft and that significantly reduces cost, weight, size and complexity of the obstacle sensing devices. Such a system would favor the use of a plurality of small, compact and directed scan devices. As such, a distributed system can be applied to a wide range of fixed wing, helicopter, UAVs and PGMs. The present invention is intended to provide for these desirable features through a distributed laser based obstacle awareness system as will become more evident from the description thereof found herein below.
In accordance with one aspect of the present invention, a distributed laser based obstacle awareness system for use on-board an aircraft comprises: a plurality of obstacle detecting sensors disposable at a corresponding plurality of locations of the aircraft for emitting laser energy from the aircraft into a predetermined region of space and for receiving return laser energy from an obstacle in the predetermined region of space; a laser source for emitting a laser beam along an optical path; a plurality of bistatic optical channels, each channel comprising a plurality of transmission fiber optic cables and at least one receiver fiber optic cable, each optical channel extending from the laser source to a corresponding obstacle detecting sensor of the plurality, the transmission fiber optic cables of each optical channel operative to direct the laser beam from the optical path to its corresponding obstacle detecting sensor of the plurality for emission into the corresponding predetermined region of space; and a light detector, return laser energy from an obstacle received by any one of the obstacle detecting sensors being propagated through the receiver fiber optic cable of the corresponding optical channel to the light detector for use in detection of the obstacle in the corresponding predetermined region of space.
In accordance with another aspect of the present invention, a distributed laser based obstacle awareness system for use on-board an aircraft comprises: a plurality of obstacle detecting sensors disposable at a corresponding plurality of locations of the aircraft for emitting laser energy from the aircraft into a predetermined region of space and for receiving return laser energy from an obstacle in the predetermined region of space; a laser source for emitting a laser beam along an optical path; an optical switch disposed in the optical path; a plurality of bistatic optical channels, each channel comprising a plurality of transmission fiber optic cables and at least one receiver fiber optic cable, each optical channel extending from the optical switch to a corresponding obstacle detecting sensor of the plurality; the optical switch operative to redirect the laser beam in a time sequence manner from the optical path to selected optical channels of the plurality, the laser beam being propagated through the plurality of transmission fiber optic cables of the selected optical channel to the corresponding obstacle detecting sensor for emission into the corresponding predetermined region of space; and a light detector, return laser energy from an obstacle in the corresponding predetermined region of space received by the corresponding obstacle detecting sensor and therefrom propagated through the receiver fiber optic cable of the selected optical channel to the light detector for use in detection of the obstacle in the corresponding predetermined region of space.